This Is How Your Thermos Flask Works

How Does a Thermos Flask Work?

Do you wonder sometimes at the genius of the thermos flask? Then buckle up. You’re about to get a behind-the-scenes look at how it actually works.

A thermos bottle has two walls with a vacuum in-between. This vacuum prevents the heat in hot drinks from leaching into the colder parts of the thermos (like the outside surface). Due to this, the liquid inside stays warm.

A thermos is a fascinating invention. Let’s discover more about who created the idea and how the flask keeps things warm (a more detailed look).

A thermos flask is not just for tea! You can also learn how to make yoghurt in a thermos flask.

How Does a Thermos Flask Work?

​Thermos flasks were invented to help prolong the time that liquids (and even food)) maintain a certain temperature. The idea for the thermos flask came about when people got quite sick of an old problem – how to keep a hot meal or drink warm when you are far away from home and hearth?

These days, we cannot imagine life without a good old thermos. Tea can be taken along on a picnic or to work. Soup can stay on the bed stand next to a loved one who feels under the weather. The list goes on.

This brings us to the next question. How does a thermos flask work?

It’s All About The Ways That Heat Can Flow

How Does a Thermos Flask Work?

To understand the inner mechanisms of a thermos flask, you need to know the number of ways that heat can flow. Bear with us. This ultimately explains everything!

Are you hunting for a new thermos flask? We have reviewed the best thermos flasks for top quality, durability, and other great features.

Conduction Convection Radiation

​Heat energy is the prime reason why a thermos flask is able to keep the temperature of its contents at the same time warmth for a long time. Learning how heat travels is essential in knowing what exactly happens inside the thermos flask when put to work. The flowing of heat happens in three ways namely conduction, convection and radiation.

Having trouble with your kettle dribbling when you try to pour water into the flask? Find out the top reasons why your kettle leaks. You will find easy solutions to solve whichever problem you are facing.

What Is ​Conduction?

​This is the process of heat transfer from an object to another object through direct contact. In other words, whenever the two objects interact or touches, there is a transfer of heat. The warmth usually transfers from the hottest object to the one that is the least hot.

What Is ​Convection?

​Convection is different from conduction in the sense that heat transfer doesn’t necessarily depend on the objects. Convection is the process that eliminates cold air when hot air rises.

As the air heats up, it becomes less dense. This allows it to rise up and stay on top of the colder air (which has a higher density). For example, this explains why, when heating hot water in a pot, the water at the top is usually hotter than a small layer at the bottom. However, at the end of the heating process, the water will have achieved an even heat distribution through convection.

A clean thermos flask is healthier, more hygienic, and will also last for years. Grab our top tips to learn how to clean a thermos flask without a fuss.

What Is ​Radiation?

​When there is an increase in the speed at which atoms move, they get unstable as they acquire more energy. This leads to the hot item letting out a certain amount of light. The light produced is just a way for the atoms to stabilize and return to their normal state. The whole process is known as radiation.

The Different Parts Of A Thermos Flask

thermos flask with unscrewed lid

The next step to understanding how this flask works is to become familiar with its design. A thermos flask consists of the following parts:

  • A screw-on stopper
  • External stainless steel or plastic casing.
  • An outer layer with a silver-coated finish (to reduce infrared radiation).
  • A vacuum between two walls.
  • An inner layer of glass.
  • Supports to keep the inner vacuum in place.
  • Extra insulation to reduce heat loss and guards the flask against external impact.

Unfortunately, since these flasks travel everywhere with us they are prone to accidents. If your flask took a knock, you can read our guide to find out how to fix a thermos flask.

How Do The Parts Work Together To Keep Drinks Hot?

In order to keep drinks at the same temperature, a thermos flask minimizes heat transfer through conduction and radiation. Convection keeps the temperature inside at an even temperature.

The vacuum insulation is very useful at eliminating heat transfer by conduction and convection. A vacuum contains no atoms whatsoever, and without atoms, not heat transfer will happen. Then there is a glass envelope that holds the vacuum. Around the glass is a vacuum space.

The glass is a very delicate part of the flask so there is a plastic or stainless steel casing to protect it. This encased glass is made of a reflective material (like a mirror) which reduces heat transfer by radiation. There is also a tight stopper that seals the contents of the flask to prevent air from coming in or going out of the thermos flask.

A Quick Summary On How A Thermos Flasks Work

  • Thermos flasks remain a popular choice for those who need to keep liquids warm for a long time.
  • These flasks can be used to store drinks and food.
  • A thermos flask is designed to work with three ways that heat is transferred.
  • These ways include conduction, convection, and radiation.
  • A thermos flask consists of parts that blend the ways to use conduction, convection, and radiation to keep liquids warm.
  • Something that plays a big role is the double-walled design of the flask. The walls are separated by a vacuum.

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About the Author Harry Thompson

Involved in home renovations throughout his life, Harry is an expert in everything to do with home and garden DIY. In his spare time, he enjoys cooking and tending to his garden.